This disclosure relates to permeability determination. In particular, but without limitation, this disclosure relates to methods and apparatuses for determining permeability of a material such as those employed in personal protective apparel.
Generally, most chemical protective clothing is tested to a common list of 21 chemicals, referred to as ‘ASTM F1001-12 Standard Guide for Selection of Chemicals to Evaluate Protective Clothing Materials’.
Standard laboratory protocols for these tests include ASTM F739 and EN 374. ASTM F739 reports breakthrough time at 0.1 μg/min/cm2 and Steady State Permeation (SSP) rate. EN 374 reports breakthrough time at 1.0 μg/min/cm2 and SSP. Companies test further chemicals, in addition to the F1001 list.
The process of permeation through a material broadly involves three stages: firstly, molecules (in liquid or gas form) are absorbed onto the outer surface of the material; secondly, the molecules diffuse across the material or multiple layers of the material; and thirdly, desorption of the molecules from the inner surface of the material occurs. If the material is in the form of a protective garment, the molecules can come into contact with the wearer from the inner surface of the material.
However, test methods can vary between batches, laboratory, methodology and apparatus etc. Indeed, the differences observed between results on open and closed-loop apparatus are discussed in the ASTM F739 Standard.